A promise

[T]he first chapter is a promise to the reader. It tells them what kind of story they’re going to be getting, and what to expect. This is true, even if you don’t intend for your first chapter to do that, because it’s the way we read. Breaking that promise can frustrate, and disappoint your reader. … By the end of the first chapter, the reader should have some sense of what the main conflict of the book is going to be. They don’t need to know all the details, but they should be able to tell the genre, have a good sense of who (what type of person) the main character is, and how their world is changing.